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MathGroup Archive 2005

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Re: ExpToTrig with Real Numbers

  • To: mathgroup at smc.vnet.net
  • Subject: [mg63341] Re: [mg63334] ExpToTrig with Real Numbers
  • From: Pratik Desai <pdesai1 at umbc.edu>
  • Date: Sat, 24 Dec 2005 16:02:52 -0500 (EST)
  • References: <200512241218.HAA15991@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Blimbaum, Jerry CIV NSWC PC wrote:

>A calculation gives me the following as a part of the output that I see
>on the screen: (i = Imaginary)
>
>-0.262484 i  Exp[-0.951249 i t] +   0.262484 i Exp[0.951249 i t]
>
>I want to apply ExpToTrig and , of course, end up with 0 for the Cosine
>part and - .262484*2  Sin [0.951249] for the Sine part ...
>
>instead I get  (which I decided to look at output with InputForm)
>
>(-0.2624844042359744*I)*Cos[0.9512492197250393*t] +
>(0.26248440423597375*I)*Cos[0.9512492197250397*t] -
> 0.2624844042359744*Sin[0.9512492197250393*t] -
>0.26248440423597375*Sin[0.9512492197250397*t]
>
>I can see from this that the coefficients and exponent numbers are very
>close but not identical  although , I think, in theory they should be.
>I'm not worried about the 10th decimal place.    How do i get the result
>I want in a general way?
>
>
>thanks....jerry blimbaum
>
>
>  
>
Here is what I get on your expression after applying ExpToTrig and Chop
I am not quite sure how you get the expression you posted

In[27]:=
$Version
-0.262484*
I* Exp[-0.951249 i* t]+0.262484 *I Exp[0.951249 i *t]//ExpToTrig//
ComplexExpand//FullSimplify//Chop//InputForm

Out[27]=
5.1 for Microsoft Windows (January 27, 2005)

Out[28]//InputForm=
(0.524968*I)*Sinh[0.951249*i*t]

Hope this helps


Regards

Pratik .

-- 
Pratik Desai 

...Moderation, as well as Regularity of Thinking, so much to be wished for in the Heads of those who imagine they come into the World only to watch and govern it?s Motion
Gulliver's Travels
by Jonathan Swift




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